In engines with electronic control unit (ECU), the primary information upon which engine control calculations are based is the engine crankshaft position. An electronic control unit comprises processors, software, and electronic hardware to process signals and perform engine operations. In most cases, crankshaft positioning relies on the respective cylinder top dead center position (TDC) as a reference point. This angle information is used to precisely time key events related to engine combustion, which in turn affects engine performance and emission. The accuracy of this information is critical, as any error may lead to engine shutdown. There are generally two possibilities for signal failure: (1) failure of a sensor, wiring, or connector resulting in a loss of signal, or (2) a high level of external noise on the sensor signal lines that interferes with the signal's zero crossing detection.
In order to identify the cylinders of a multicylinder internal combustion engine, most ECUs require signals from a camshaft sensor and a crankshaft sensor. Most engines are configured such that the crankshaft undergoes two revolutions for every single revolution of the camshaft. Typically, the engine crankshaft comprises a crank wheel that is mechanically coupled to the crankshaft. The crank wheel comprises a plurality of elements with at least one reference element, such as a missing gap, oversized element, an attached element or differently configured or shaped element, and the like. Crank sensors are positioned proximate to the crank wheel to produce signals upon passage of the elements. This signal information is sent to the ECU, and the ECU determines the position of the crankshaft by counting the number of elements after the marking element, this is also referred to as synchronization. This enables the ECU to know 360 degree position of the crankshaft. The ECU must then use the signal of the cam sensor to determine if the crankshaft is in the first revolution or the second revolution. Thus, if there is a break in the information from the crankshaft sensors, the ECU will lose the position of the crankshaft and will not know whether the crankshaft is in the first revolution or the second revolution. Consequently, the ECU cannot determine which cylinder should be injected with fuel or not (e.g. with respect to a typical diesel engine, whether the cylinder is in the power stroke or exhaust stroke). If a break in the crank sensor information occurs, the engine may be rendered incapacitated.
One attempt to minimize this problem has been to provide two crank sensors; the idea being that one crank sensor acts as a back-up sensor to the other. According to this configuration, the ECU will receive signal information from one of the sensors. If a failure happens, the ECU will effectuate a “switchover” to the other sensor. Having a redundant sensor does address the problem somewhat, but there remain important performance issues. In the event of a failure of the active sensor, the ECU loses engine position and is incapable of calculating speed. The ECU must stop fueling until synchronization is complete on the redundant sensor. The synchronization of the crank sensor signals and determination of the proper crank revolution requires time. The cessation of fuel injection during this time dramatically decreases engine performance.